This invention relates to a method for producing architectural and engineering drawings on a pen plotter as part of a computer aided drafting (CAD) system such that the CAD plots are accurately aligned, or registered, with other CAD plots or manually produced drawings for use on the same project.
The use of CAD Systems has become more common in the production of architectural and engineering drawings because of the speed, accuracy, and repeatability of such systems. The drawings or plots produced by such systems are most often generated either on electrostatic or pen plotters. The present invention is intended for use in conjunction with pen plotters, which are generally more efficient in producing translucent overlay drawings. Specifically, the present invention is intended for use with pen plotters which primarily use the physical movement of the plotting medium to produce the plot, such as the Hewlett Packard 75xx series.
It is still necessary when producing architectural drawings on CAD Systems to integrate or accommodate manually produced drawings. For example, some designers and consultants must manually add their design portions to pre-existing CAD plots (base drawings) as part of the design routine. Or, the capacity of the CAD System to accommodate simultaneous design efforts may be exceeded, forcing some designers to manually create their drawings.
It is essential that a method exist for precisely aligning each separate project drawing or CAD plot (overlay). That is, when the various overlays are viewed together, or in conjunction with a base drawing, each common design element or reference point must be physically located at the same point on each drawing so that the designer or viewer will get an accurate picture of the overall design and how the various design features fit together. For example, when the drawings or plots are ready for inclusion into the contract documents, a method must be available for aligning the overlays which are then reproduced or photographed as a composite design drawing.
At present, the typical method for producing registered plots on pen plotters which move the plotting medium is to use an unpunched translucent drafting sheet. The sheet is placed on the plotter and then the plotter is directed to plot two or three or more cross-hair targets (registration marks) at or near the borders of the sheet. Each sheet which is to become a base or overlay drawing on the project must be plotted with consistent reference to these registration marks.
After the sheets are plotted with the registration marks, they are placed, on a light table, in a standard 7-pin bar registration punch. The sheet is then secured, punched, and the registration marks are also placed on the light table in exact alignment with those on the sheet. Each successive sheet on which registration marks have been plotted can then be placed on the punch, visually aligned with the registration marks on the light table and then punched with the seven registration holes. The result will be a succession of sheets on which the registration marks are physically located in the same place with respect to the bar pin holes. The overlays can then be simultaneously viewed in registration when placed on a standard 7-pin registration bar.
The post-punch method just described works well but is prone to human error. An error of even one-sixteenth of an inch in visually aligning the registration marks will result in an out of registration plot. This poses a significant problem in large projects which can involve more than two hundred punched drawings.
Existing pre-punch and post-punch production and registration methods are generally described in "CAD PRODUCTIVITY A SYSTEMS APPROACH" (E. I. DuPont de Nemours and Co. 1985).
U.S. Pat. No. 4,440,080 discloses a technique for registering multiple color screens on a flat bed printer.
U.S. Pat. No. 3,398,637 relates to an apparatus for optically registering printing and model surfaces.
U.S. Pat. No. 3,763,730 discloses an optical hole punch for registration of printed circuit board artwork.
Japanese Pat. No. 55-82009 describes a system for optically aligning printed circuit board artwork.
What is needed, then, is a means of producing multiple overlay CAD plots and aligning them with each other and with manually generated drawings with consistent precision while using a conventional pen plotter and registration bar.